1. Field of the Invention
This invention relates to automatic assembly techniques, and more particularly relates to automatic sensing of the airflow at a hole, and moving a pin laterally to a position within the airflow where lateral forces of the sensed airflow most closely approach a null over the hole, to position the pin at the insertion point for the hole.
2. Description of the Prior Art
A recurring problem in automated assembly is the classic "pin-in-hole" problem wherein a cylindrical pin must be inserted into a cylindrical hole of closely matching diameter. A traditional approach is to put chamfers on the hole, the pin, or both, and to use compliant fixturing for gripping the pin. This approach fails if the pin and hole axes are separated by more than the capture region of the chamfers. This approach also fails in the case of flexible or curved pins, such as wires or filaments. Even the addition of vacuum suction will not extend the capture region of the hole much beyond the chamfer, that is, beyond a "virtual chamfer". The addition of vacuum suction to the hole can increase the capture region beyond that defined by mechanical chamfers, but due to the mass of large pins or fragility of small ones it may be difficult to achieve vacuum sufficient to increase the capture region of the hole significantly. Moreover, the geometry of the insertion problem may make it difficult to create a pressure differential across a hole which causes aiding airflow into the hole, while the same geometry may easily allow the opposite differential which causes resisting airflow from the hole. It might be outside the normal precision of the robot to go directly to the insertion position in open loop mode. It is difficult to achieve the optical and mechanical precision necessary for a closed loop approach, even with a vision-equipped robot, because the necessary precision is difficult to achieve and because the robot gripper, and indeed the pin itself, may obscure the hole.
The following patents are representative of the prior art:
U.S. Pat. No. 3,667,103, Edwyn H. Petree, APPARATUS FOR INSERTING TERMINALS IN AN APERTURED PLATE, June 6, 1974, shows the use of vacuum together with vibration to pull pins into chamfered holes in a plate. PA0 U.S. Pat. No. 4,155,169, S.H. Drake et al, COMPLIANT ASSEMBLY SYSTEM DEVICE, May 22, 1979, shows the use of a compliant gripper to ease insertion of a pin into a hole. PA0 U.S. Pat. No. 4,485,453, Taylor, DEVICE AND METHOD FOR DETERMINING THE LOCATION AND ORIENTATION OF A DRILLHOLE, Nov. 27, 1984, shows the use of a drill bit as a probe for a robot to use in determining the location of a drillhole. PA0 German Patent No. DE28 34 6984, Petermann et al, Feb. 14, 1980, shows a vacuum assisted insertion technique for electrical components.
The prior art shows the use of vacuum in pin-in-hole operations, shows the use of a compliant gripper in pin-in-hole operations, and shows the use of instrumented grippers. The prior art thus shows the use of the chamfer capture region to capture the pin, and shows vacuum enhancement of the chamfer capture region (virtual chamfer) but fails to show any automatic techniques in a detection region, in the outer vicinity of the hole, which the robot can follow to position the pin at the insertion point for the hole. The prior art does not show and does not suggest the inventive combination, which allows the robot to respond to the forces of airflow through a hole, using sensors closely associated with the pin, or the pin itself, as a probe to direct and control motion of the pin to the insertion point within the capture region of the hole, perform the insertion, and detect successful insertion.
Nor does the prior art teach the method of positioning the pin in the general vicinity of the selected hole in open loop mode; searching for a null in lateral airflow forces in closed loop mode, to determine the insertion point; inserting the pin in open loop mode; and detecting successful insertion.